The present invention relates generally to the testing of electronic circuit boards or subassemblies, and is particularly concerned with a multilayer printed circuit board or translator board for connecting test points on a unit or circuit board under test to the testing electronics of automatic test equipment, and to a method of manufacturing such a board.
The electronics manufacturing industry has a continuing need for production testing of electronic subassemblies. Automatic test equipment (ATE) is typically used to test the components and circuit interconnections on printed circuit boards after assembly, to determine whether any of the components are defective and whether there are any manufacturing defects such as short circuits, open circuits, or incorrectly installed components. The ATE comprises a large, computer based system and is expensive to purchase and to support and maintain. Testing costs are a significant portion of production costs in the electronics industry.
Most ATE systems are general purpose and can be used to test a variety of different electronic products. However, for each electronic product to be tested, a unique or one-of-a-kind test fixture must be provided to electronically interconnect the test object, called a unit under test (UUT), with the ATE test set electronics. Additionally, a unique, one-of-a-kind test program must be created to describe the UUT components and circuitry and the interconnections to the ATE computer.
Text fixtures are rectangular shaped, box-like assemblies that include what is called a "bed of nails" or spring probes on top of the assembly for contacting test points on a UUT, and an ATE interface panel on the bottom for connection with the ATE test set electronics. Additionally, some means is provided for electronically interconnecting the spring probes to the interface panel according to the specific testing requirements. In wired test fixtures, insulated wires are used to provide the required interconnections. Because several hundred, and sometimes thousands, of interconnections are required in the test fixture, wiring is a very labor intensive and error prone process. The large number of wires also degrades test signals and limits the speed at which components can be tested. Long wire lengths also result in test signal degradation and cause undesirable "cross-talk" or noise that can result in unstable or erroneous test results.
Wireless test fixtures are technically superior to wired test fixtures but more expensive to produce. In this case, the required interconnections are provided in a multi-layer printed circuit board (PCB). Double ended spring probes contact the UUT at one end, and contact plated pads on top of the printed circuit board or interface board at the other end. The bottom layer of the PCB has plated pads which interface with the ATE terminals.
Interconnections between the top pads and bottom pads are provided by predetermined printed wiring on the various layers of the PCB. The printed wiring is considerably shorter in length and less susceptible to noise and cross-talk than the wires used in wired test fixtures. Wireless test fixtures are technically superior to wired test fixtures but are more expensive and also more time consuming in design and fabrication, since a one-of-a-kind PCB must be designed and fabricated for each new circuit board to be tested.
Because of the requirement of a unique test fixture for each different electronic product, one or more new test fixtures are required for production support each time a new electronic product is designed. Such test fixtures are expensive and time consuming to design and manufacture. This requirement is the most common cause of delay in marketing new electronic products.
U.S. Pat. No. 5,216,361 of Akar et al. describes a circuit board test system with a wireless test fixture or receiver for providing the necessary connection between an ATE system and UUT. In this case, a PCB or translation board defines a prescribed signal mapping for interconnecting I/O pins of ATE pin cards to the underside of a fixture to be tested. A different translation board with a different mapping is required for different units to be tested.
Currently, as noted above, a completely new PCB or interconnecting panel must be designed and fabricated each time a new electronic product is designed. The design and fabrication of such PCBs currently takes two to three weeks, considerably delaying the introduction of new electronic products.